This is a firmware that doesn't require any compiling. It can be downloaded from its Geekhack thread. This is for those who want to create their own layouts, layers, macros and other stuff without touching any code.

Bpiphany's branch of Hasu's tmk_keyboard. Includes all Bathroom Epiphanies Costar Replacement controllers. The core libraries may not be up to date with Hasu's repository at all times. It's however easy to merge his core into bpiphany's repository.

Flashing the controller

There are different software tools to insert, or flash, a firmware hex-file onto the controllers. They can be a bit tricky to set up correctly on locked down operating systems. Google the Internet if trouble arises. Suggested search words are "flash AVR controller dfu-programmer/FLIP Windows/Linux/OSx". Find a good tutorial out there. You may need to add rules, libraries or/and be the super user of your system to be able to do these things.

To enter the bootloader mode of the controller the reset signal of the ATmega chip needs to be triggered. On the replacement controllers there is a magnetic switch which will do this. While powered run a magnet nearby the little glass tube. Usually the switch can even be heard operating. Your computer/flashing tool should recognize that there is a controller in bootloader mode waiting for instructions.

dfu-programmer

The tool dfu-programmer is available both for Linux and Windows. (Mac as well?)

FLIP

FLIP is Atmel's own tool to write hex files to AVR controllers. It should work on Windows, and is GUI front ended for those who doesn't feel like using a terminal. Its Linux version seem to be outdated.